A sampling device generally comprises a probe for sampling gas and a pipe for transmitting the gas samples taken to a system for exploiting samples, such as a gas analyzer.
Generally, gas sampling with a view of analyzing their compositions, constitutes a key step, in particular when the gases to be sampled are hot and comprise a high proportion of water in the form of vapor. In this context, it is indeed sensitive to perform reliable analyses, and current sampling devices require frequent maintenance operations.
In particular, sampling hot and wet gases raises a condensation issue. Indeed, the dew point, also called “condensation temperature” of the water contained in hot gases having a high rate of water vapor can reach several dozens, even several hundreds of degrees Celsius. The result is that at ambient temperature, the water vapor contained in these gases may condensate in droplets which deposit onto the walls in contact with the gases. If the gases sampled comprise molecules soluble in water, the molecules tend to be caught and to dissolve in the droplets. The result is that the compositions of the gases which are transmitted to the exploiting device do not correspond to the compositions of the gases sampled. The gas sampling device may therefore affect the compositions of the gases sampled and therefore the quality of the measurements taken if the system which exploits the samples of gases sampled is a gas analyzer. In addition, the droplets formed on walls may cause corrosion phenomena, and all the more since the droplets may be acid due to gas molecules which are dissolved therein. The gas sampling device may therefore also affect the operating costs and conditions of the system into which it is integrated.
Some gas sampling devices are designed to maintain the gases sampled at a temperature higher than the dew point of the water vapor contained in the gases sampled, both in the probe and the pipe. Thus, some of these devices are designed to maintain the sample of gases sampled at a temperature which can reach one or two hundred degrees Celsius. Such devices therefore have a high manufacturing cost, due in particular to the complexity of the pipe which must be heated and the necessary presence of temperature regulators, also high operating and maintenance costs due in particular to the energy required to maintain the device at a relatively high temperature. In addition, these devices imply that the exploitation system is also designed to operate at the same temperature.
Other sampling devices comprise a heated probe and a device for drying the gas sample taken. Such a drying device implements membranes, or a cooling means. These devices also have high manufacturing and maintenance costs due to the presence of the drying device which may require frequent maintenance operations with some gases to be sampled. In addition, these devices denature the sample taken, since they modify the composition thereof.
Other sampling devices provide to dilute the sample taken in another gas, such as dust free air. To that end, these devices comprise a probe which is not necessarily heated, a Venturi system performing sucking and diluting the gas samples, a not heated pipe and a system supplying the dilution gas under pressure at high flow. These devices also have the drawback of denaturing the sample taken since its composition is also modified due to its dilution in another gas, and all the more since the dilution gas may in addition bring impurities. In addition, if the sampling device is linked to an analyzing device, the latter must be very sensitive to be able to detect low quantities of gaseous components due to the dilution.
It is therefore desirable to be able to take gas samples without condensation phenomenon, but without denaturing them or without needing to maintain them at high temperature, to dry them, or to dilute them.